Tree, Shrub Dangers

By TOM STEVENSONBy TOM STEVENSONJune 1, 1979

Several kinds of insects and diseases attack trees and shrubs about now; some are quite serious.

Sycamore anthracnose is favored by cool, wet spring weather. The first visible symptom is the sudden browning of leaves or clusters of leaves. If the weather remains cool and wet, most of the leaves turn brown and fall off. Small twigs are also attacked and killed. In addition to spoiling its attractiveness, the disease weakens the tree so it becomes prey to many other troubles, particularly drought injury. By the time the damage is apparent, it's too late to spray effectively. To prevent large numbers of the spores from carrying over to next spring, rake and burn all leaves and diseased twigs. Fertilizing the tree will help overcome damage.

Scab is the major disease of crab-apples and apples. while others have a lot of resistance. The disease thrives in cool, wet spring weather and is most destructive during rainy periods from the time the buds show color until about four weeks after the petals fall. The foliage, stems and fruit are affected. Damage can be prevented by keeping the expanding buds, leaves and young fruits covered with an effective fungicide, a job for a professional. Probably the best control is to replace the tree with one that has more resistance.

Leaf miners are tiny insects that feed between the surfaces of leaves. Look for whitish blotches, or dark grayish to white serpentine mines, or winding trials in the upper surface of infested leaves. Damages foliage may lose its vigor and ultimately be reduced in size, with loss of healthy color. Eggs are laid either in the leaf tissue or on the surface by small flies that vary from 1/32 to 1/16 inches in length. For a week or ten days before egg-laying the females use their ovipositor to puncture the tissue in the upper surface of newly forming leaves, mainly near the edges. Leaves seriously damaged in this manner frequently become stunted and badly distorted. Infested holly leaves may drop to the ground before over-wintering adult leaf miners emerge. It helps to gather up and destroy such leaves. Emergence coincides with development of new leaves. With boxwood and small holly plants it will pay to pick off and destory leaves infested with miners before the flies emerge.

Damage from tent caterpillars has occured since early Colonial times. At intervals of about 10 years the damage is quite serious. After hatching, the caterpillar build their tents - tiny at first, but larger as the caterpillars grow. The best control is to pick and destory the tents while they're small. Spraying with Sevin can be effective while the caterpillars are still quite small.